I went ahead and checked out the map. My first suspicion was that the spawns on the ground level were the issue, and that's what it was.

To fix, just raise the ground-level spawns in the air. 16 or 32 units is fine, as long as they are up. This should be a general rule of thumb for making spawns to prevent this issue entirely. Its just so the game doesn't get confused on - what I'm guessing - what surface to drop the player on.

Spawns spawn the player at the highest point they ecnounter on something solid below them. When they're touching the ground, especially on uneven ground like props or displacements, sometimes they think that's whatever's under that brush, like the skybox.